This invention relates to a ball valve.
In one type of ball valve heretofore in use, the valve seat is formed so as to have, in combination, the functions of valve seat, packing and retainer, and is highly effective in view of simplifying valve assembly.
However, the seat becomes very complicated in shape and structure making it exceedingly difficult to machine the spherical surface of the valve seat. Consequently, the valve seat of the type described has the disadvantage that maintaining machining accuracy in individual parts becomes difficult and not only the valve seat and its vicinity are subject to leakage, but also machining becomes troublesome, resulting in difficulty in reduction of production cost.
When the valve seat becomes worn or damaged, the whole of the valve seat, high in machining cost, has to be replaced with the disadvantageous result in increased repair cost.